1. Field of the Invention
The present invention relates generally to monitoring systems employing optical fibers and more particularly to those involving the monitoring of aqueous infiltration.
2. Description of Related Art
The monitoring of corrosion effects on mechanical equipment when operating in a sub-sea or harsh environment is a necessity in many situations. For example such monitoring includes (i) in-situ monitoring the health of aerospace, civil and marine structures for structural deformation effects and the effects of corrosion and water or chemical infiltration into structural material systems including Fiber Reinforced Plastic (FRP) composite material, (ii) monitoring of the long term health of aging aircraft fuselage structural integrity, (iii) monitoring pressure on composite FRP structures which include mast and spar flexing, sail pneumatic pressure and hull deformation and moisture or chemical infiltration or change in any composite material structure.
The following references U.S. Pat. No. 5,258,930 November, 1993 Fukuyoshi et al: U.S. Pat. No. 5,389,411 February, 1995 Cohen: U.S. Pat. No. 6,080,982 June, 2000 Cohen: U.S. Pat. No. 5,165,283 November, 1992 Kurtz et al: U.S. Pat. No. 5,181,423 January, 1993 Phillips et al: U.S. Pat. No. 5,187,475 February, 1993 Wagener et al: U.S. Pat. No. 5,196,845 March, 1993 Myatt: U.S. Pat. No. 5,278,442 January, 1994 Prinz et al: U.S. Pat. No. 5,515,041 May, 1996 Spillman et al. Other references: A. Martin, “A Novel Optical Fiber-Based Strain Sensor”, IEEE Photonics Technology Letters Vol. 9 No. 7, July 1997: D. C. Inder, “Evaluation of a low-cost fiber-based strain sensor”, SPIE Vol. 3670.0277-789X/99, March 1999: o. Suzuki, “POF-Type Optic Humidity Sensor and Its Application”, IEEE 0-7803-7289-1/02: K. Broadwater, “Experimental and Numerical Studies In the Evaluation of Epoxy-Cured Fiber Optic Connectors”, 2000 Electronic Components and Technology Conference, September 2000: J. Mrotek, “Diffusion of Moisture Trough Optical Fiber Coatings”, IEEE, JNL 0733-8724/01, July, 2001: K. Cooper, “Optical Fiber-Based Corrosion Sensor Systems for Health Monitoring of Aging Aircraft”, IEEE, 07803-7094-5/01, May 2001: B. Degamber, “Remote Process Monitoring Using Optical Fibre Sensors”, IEEE, 0-7803-7454-1/02, January 2002: N. Yonemoto “Multi-functional Sensing for High-sensitivity Detection of Initial State of Iron Rust”, IEEE Instrument and Measurement Technology Conference, May 1988: Y. Chuah, “Wireless Telemetry System for Strain Measurement”, IEEE, 0-7803-5957-7/00, July 2000: Royal Navy Procedure UK-DEF STAN 02-304 Part 4/Issue 2 (Apr. 1, 2000) describe related applications.
In addition, the following US Patents describe other related applications, U.S. Pat. No. 5,995,686 to Hamburger et al., U.S. Pat. No. 6,466,323 to Anderson et al., U.S. Pat. No. 5,005,005 to Brossia et al., U.S. Pat. No. 4,634,856 to Kirkham, and U.S. Pat. No. 4,866,265 to Hohne.
There is a particular problem associated with underwater apparatus including docks, ships, barges and other equipment associated therewith as one must generally assume a certain “shelf/operational life” for various instrumentation and or components in order to prevent the apparatus shutting down or encroaching on design limits due to damage from water or other seepage. For example, in the case of some navy ship propulsion shafts, such shafts are automatically taken out of service or limited in operational service after approximately 7 years in use. Sometime the infiltration is close to damaging the components and sometimes it isn't. However, to be sure, to date, the only option is to take the equipment out of service. This is an expensive and often unnecessary waste of time if there has been no damage or no initiation of corrosion.
An easier method to monitor such applications and remote equipment would be highly desired but has not heretofore been developed.